Hello all, new to the forum but I've been lurking around for quite a while trying to figure out things for myself. I'm very green at circuitry on this level but am actively self-teaching to learn more. I understand the basics of a lot of the most used components in circuit boards, but I'm stumped on my latest endeavor. I recently had a car alarm installed that has a 3V output powering a red LED but it's very dim and can't be seen during the day and barely at night - so, I grabbed a 5V bright blue LED to put in place. Of course, I knew the module wouldn't power it to the level I wanted, so I integrated a small board with a 2N2222 transistor and 350 ohm resistor on the collector side. Problem I have is that the alarm module blinks the led once every 5 seconds and it's barely a blink (split second) so it's not powering my "aftermarket" LED the way I would like. I believe including a 555 timer may help in my efforts to get my bright blue LED to "hold" the blink for at least a second, but every other time I've used a 555 timer, the control voltage had to be constant (not a pulse), not sure how to integrate (another transistor?) the timer into my circuit. To sum it up: in my ideal world, I would like to have blink my bright blue LED every 2-3 seconds from the alarm's factory slow blink 3V output. I know I just butchered my explanation of this and I don't have a schematic but hopefully it's enough to understand. Any input is greatly appreciated.
Thanks!
Clint

 

Here's a schematic of what I have - not sure how to make the pulsing 3V output of the alarm module trigger the transistor long enough to light my blue LED. Correction to my first post, it's actually a 330 ohm resistor. I know all this may seem trivial just for an LED, but it's what I'm doing right now. Again, thanks for any input

 

The reason you aren't getting answers is that you asked for too much, completely changing all the timing from a tiny pulse.
What you drew is a pulse stretcher, but it goes more like this:
There is a way to do it with a 555 timer and get a sharp, "off" for the LED, but that's more work.
Good enough to have a sharp, "on" then just let it fade away?
(The 1M resistor is probably a bit high.)

 

Thanks a lot, however what is this symbol? I've not come across it yet and am not afraid to ask:



Sharp "on" and fade away is just fine - I'll skip the 555 for now

 

That's an N-channel enhancement type mosfet.
They are very good at low voltage drop in the LED circuit and very good about gate leakage current. That's why I can stick a million ohms in there and expect the gate to work.
You need one that's good for at least 60 volts in a car.
Personally, I would go for a 100 volt n-channel mosfet. Cars can get so hinky about voltage spikes!
Anything on this page will do:
http://www.mouser.com/Semiconductor...w78k9Z1yw78izZ1yw76b4Z1yw78faZ1yw764iZ1yw78f4

 

That's an N-channel enhancement type mosfet.
They are very good at low voltage drop in the LED circuit and very good about gate leakage current. That's why I can stick a million ohms in there and expect the gate to work.
You need one that's good for at least 60 volts in a car.
Personally, I would go for a 100 volt n-channel mosfet. Cars can get so hinky about voltage spikes!
Anything on this page will do:
http://www.mouser.com/Semiconductor...w78k9Z1yw78izZ1yw76b4Z1yw78faZ1yw764iZ1yw78f4

Thanks again for your help, this is great info